Gas production apparatus

ABSTRACT

A gas production apparatus is provided which include: an element laminate having a light receiving section on one side and a conductive substrate on the other, in which laminate a plurality of elements, each including a semiconductor thin film with pn junction, are so laminated on each other as to connect in series to each other; a hydrogen gas generator formed on a surface of a first element located on the light receiving section side; a first electrolysis chamber including the hydrogen gas generator; an oxygen gas generator formed on a back surface of the conductive substrate; a second electrolysis chamber including the oxygen gas generator; and an ion-permeable but gas-impermeable diaphragm provided between the first and second electrolysis chambers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/JP2014/057583 filed on Mar. 19, 2014, which claims priority under 35U.S.C. §119(a) to Japanese Patent Application No. 2013-068993 filed onMar. 28, 2013. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

BACKGROUND OF THE INVENTION

The present invention relates to a gas production apparatus.Specifically, the present invention relates to a gas productionapparatus that produces hydrogen and oxygen by decomposing water byreceiving light.

In the prior art, as one of the modes of using solar light energy as arenewable energy, hydrogen production apparatuses have been suggestedwhich produce hydrogen used for fuel cells and the like by using aphotoelectric conversion material used for solar cells and utilizingelectrons and holes obtained by photoelectric conversion for adecomposition reaction of water (for example, see JP 2012-177160 A andJP 2004-197167 A).

In both of the hydrogen production apparatuses disclosed in JP2012-177160 A and JP 2004-197167 A, a photoelectric conversion portionor a solar cell, in which two or more pn junctions generating anelectromotive force when solar light is incident thereon are connectedto each other in series, is provided; an electrolytic solution chamberis disposed at the lower side of the photoelectric conversion portion orthe solar cell that is opposite to a light receiving surface whichreceives solar light on the upper side of the photoelectric conversionportion or the solar cell; and the inside of an electrolysis chamber isdivided by an ion-conductive partition or diaphragm, and the documentsdisclose that by the electric power that is generated in thephotoelectric conversion portion or the solar cell by the received solarlight, water is electrolyzed, and hydrogen is generated.

According to JP 2012-177160 A, because the hydrogen production apparatuscan also adjust the orientation of the light receiving surface withrespect to the solar light, the amount of incident light that will besubjected to photoelectric conversion can be increased, and hydrogengeneration efficiency is not reduced.

Furthermore, according to and JP 2004-197167 A, because the hydrogenproduction apparatus electrolyzes water by using electrode plates, whichare connected to a p-type semiconductor and an n-type semiconductor ofthe solar cell, as a positive electrode and a negative electroderespectively, the efficiency of conversion of solar energy into hydrogencan be improved.

SUMMARY OF THE INVENTION

In both of the hydrogen production apparatuses disclosed in JP2012-177160 A and JP 2004-197167 A, in the electrolysis chamber that ison the side opposite to the light receiving surface of the photoelectricconversion portion or the solar cell, that is, in the electrolysischamber that is on the back surface side of the photoelectric conversionportion or the solar cell, hydrogen and oxygen are generated as a resultof electrolysis of water. Therefore, if the generated gas such ashydrogen or oxygen adheres to a gas generation surface of the gasgenerating electrode of the photoelectric conversion portion or theelectrode plate of the solar cell and stays between the gas generationsurface and an aqueous solution such as an electrolytic solution, acontact area between the gas generation surface and the aqueous solutionis reduced, and this leads to a problem in that the efficiency ofgenerating gas such as hydrogen and oxygen is reduced.

Although the hydrogen production apparatuses disclosed in JP 2012-177160A and JP 2004-197167 A show high gas generation efficiency particularlyat the initial gas generation stage, with the passage of time, theamount of gas staying between the gas generation surface and the aqueoussolution such as an electrolytic solution increases. As a result,because a contact area between the gas generation surface and theaqueous solution is reduced, the efficiency of generating gas such ashydrogen and oxygen greatly decreases, and this leads to a problem inthat gas cannot be stably generated.

An object of the present invention is to solve the aforementionedproblems of the prior art and to provide a gas production apparatuswhich can maintain high gas generation efficiency at the initial gasgeneration stage and even after the passage of time, and can stablyproduces hydrogen gas and oxygen gas as high-purity gases completelyseparated from each other.

In order to achieve the above object, the present invention provides agas production apparatus comprising: an element laminate in which aplurality of elements, each having a light receiving portion andincluding a semiconductor thin film with pn junction, are so laminatedon each other as to connect in series to each other; a hydrogen gasgenerator which is formed on a surface of a first element among theplurality of elements and generates hydrogen gas, the first elementbeing positioned at one end of the element laminate; a firstelectrolysis chamber which includes the hydrogen gas generator andcontains an aqueous electrolytic solution in contact with the hydrogengas generator, and the hydrogen gas generated; an oxygen gas generatorthat is formed on a back surface of a conductive substrate, on which thesemiconductor thin film of a second element among the plurality ofelements is formed, and generates oxygen gas, the second element beingpositioned at another end of the element laminate; a second electrolysischamber which includes the oxygen gas generator and contains an aqueouselectrolytic solution in contact with the oxygen gas generator, and theoxygen gas generated; and a diaphragm which is ion-permeable butgas-impermeable, and is provided between the first electrolysis chamberand the second electrolysis chamber.

The hydrogen gas generator is preferably provided with a hydrogengeneration surface which is formed on a surface of the semiconductorthin film of the first element.

The first element is preferably composed of a plurality of sub-elementswhich are disposed on the second element discretely with respect to thesecond element.

Preferably, the plurality of sub-elements each have an element areasmaller than that of the second element.

The oxygen gas generator is preferably provided with an oxygengeneration surface which is formed on the back surface of the conductivesubstrate and inclined upward along a flow direction of the aqueouselectrolytic solution in the second electrolysis chamber.

It is preferable that the semiconductor thin film includes a CIGS-basedcompound semiconductor.

It is also preferable that the semiconductor thin film includes aCZTS-based compound semiconductor.

Preferably, the semiconductor thin film has an absorption wavelengthedge equal to or greater than 800 nm.

The gas production apparatus preferably further comprises a hydrogengeneration promoter provided on the hydrogen generation surface of thehydrogen gas generator.

Preferably, the hydrogen generation promoter is platinum.

According to the present invention, it is possible to maintain high gasgeneration efficiency at the initial gas generation stage and even afterthe passage of time and to stably produce hydrogen gas and oxygen gas ashigh-purity gases completely separated from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing an example of agas production apparatus according to an embodiment of the presentinvention.

FIG. 2 is a top view of the gas production apparatus shown in FIG. 1.

FIG. 3 is a flow chart showing an example of a process of manufacturingthe gas production apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the gas production apparatus according to the presentinvention will be specifically described based on a preferred embodimentshown in the attached drawings.

The present invention is an apparatus producing hydrogen and oxygen byusing, as an electrode for decomposing water, a semiconductor thin filmhaving a pn junction and used in a solar cell or the like. With a singleelement constituted with, for example, a pn junction-semiconductor thinfilm, a conductive film, and a support substrate, the ability tophotolyze water is insufficient, and an electromotive force equal to orhigher than a starting voltage of electrolysis of water is not obtained.Therefore, in the apparatus of the present invention, a plurality ofelements are connected to each other in series in order that theelectromotive force may be increased, and the total electromotive forceof the elements may become equal to or higher than the starting voltageof electrolysis of water. Furthermore, in the apparatus of the presentinvention, through a photolysis reaction of water, hydrogen is generatedfrom the side of a light receiving surface of the elements, oxygen isgenerated from the side of a surface opposite to the light receivingsurface, and thus the hydrogen and oxygen generated by the decompositionof water are separately collected. In this way, the apparatus produceshydrogen and oxygen at a high purity. As the method for connecting theelements to each other, a method is preferably used in which the elementthat will be laminated on an element having a large element area isconstituted with a plurality of sub-elements having a small elementarea, and the sub-elements are discretely laminated on the elementhaving a large element area.

First, characteristics of the gas production apparatus according to theinvention will be described in comparison with the gas productionapparatus of the prior art.

As described above, in the prior art, all of the surfaces (gasgeneration surfaces) of the electrodes for electrolysis that generategas are disposed on the back surface side of the photoelectricconversion portion that is opposite to the light receiving surfacereceiving solar light. In contrast, the present invention ischaracterized in that the hydrogen generation surface and the lightreceiving surface receiving solar light are disposed on the same side.In this way, if the hydrogen generation surface is disposed on the sideof the light receiving surface, desired effects, such as being able tomaintain high gas generation efficiency regardless of the passage oftime and being able to stably produce hydrogen gas and oxygen gas, areobtained.

FIG. 1 is a cross-sectional view schematically showing an example of agas production apparatus according to an embodiment of the presentinvention, and FIG. 2 is a top view of the gas production apparatusshown in FIG. 1.

First, as shown in the drawings, a gas production apparatus 10 has anelement laminate 12 in which a plurality of elements, in each of which asemiconductor thin film having a pn junction is formed, are verticallylaminated on each other in series; a hydrogen gas generation portion 14a which is disposed at an open end of the element positioned at theupper end of the element laminate 12; an oxygen gas generation portion14 b which is disposed at an open end of the element positioned at thelower end of the element laminate 12; a container 18 constituting anelectrolysis chamber 16 which contains an aqueous electrolytic solutionAQ in contact with the two gas generation portions 14 a and 14 b, andhydrogen gas and oxygen gas that are generated in the gas generationportions 14 a and 14 b respectively; and a diaphragm 20 which partitionsthe electrolysis chamber 16 into two electrolysis chambers 16 a and 16 bincluding the gas generation portions 14 a and 14 b respectively.

The element laminate 12 is for generating hydrogen and oxygen through aphotolysis reaction of water by receiving light such as solar lightthrough a light receiving surface, and has a plurality of (two in theexample illustrated in the drawings) pn junction elements 22 and 24 thatare vertically laminated on each other in the drawing. Hereinafter, as atypical example, the number of the pn junction elements connected toeach other in series is described as two. However, as long as the totalelectromotive force of a plurality of pn junction elements is equal toor higher than the starting voltage of the electrolysis of water, thenumber of the pn junction elements is not limited to two as in theexample illustrated in the drawings. It goes without saying that thenumber of the pn junction elements may be arbitrarily set.

The pn junction elements 22 and 24 are photoelectric conversion elementswith a laminated structure having the same constitution as that of asolar battery cell used as a solar cell. The pn junction elements 22 and24 are for generating electrons and holes through photoelectricconversion by receiving light such as solar light through the lightreceiving surfaces, and sending the generated electrons and holes to thegas generation portions 14 a and 14 b respectively.

The pn junction element 22 on the substrate side of the element laminate12, that is, on the lower side in the drawing is an oxygen generationelement generating oxygen and has a conductive plate 26, a photoelectricconversion layer 28, and a buffer layer 30 that are laminated on eachother in this order from the lower side toward the upper side in thedrawing. The pn junction element 22 has a transparent conductive film32, which becomes an upper electrode, on the buffer layer 30.

The pn junction element 24 on the light receiving surface side of theelement laminate 12, that is, on the upper side in the drawing is ahydrogen generation element generating hydrogen. The pn junction element24 is an assembly of a plurality of (nine in the example illustrated inthe drawings) small-sized pn junction elements 24 a. The ninesmall-sized pn junction elements (hereafter also referred to as“sub-elements”) 24 a are disposed on the pn junction element 22,specifically, on the transparent conductive film 32 discretely, that is,in the form of scattered islands. In the pn junction element 24 (24 a),the transparent conductive film 32, the photoelectric conversion layer28, the buffer layer 30, and a transparent protective film 34 arelaminated on each other in this order from the pn junction element 22 onthe lower side toward the upper side in the drawing. On the transparentprotective film 34, a promoter 36 for generating hydrogen is formed inthe form of scattered islands.

The transparent conductive film 32 functions as a lower electrode in thepn junction element 24 (24 a) and functions as an upper electrode in thepn junction element 22. Therefore, it can be said that the transparentconductive film 32 functions as an electrode common to both the pnjunction elements 22 and 24 (24 a). Since the transparent protectivefilm 34 constitutes an upper electrode of the pn junction element 24 (24a), a transparent conductive protective film is used as the transparentprotective film 34.

Accordingly, it can be said that the pn junction element 24 (24 a) isconstituted with the transparent conductive film 32, the photoelectricconversion layer 28, the buffer layer 30, the transparent protectivefilm 34, and the hydrogen generation promoter 36.

Incidentally, the sub-elements 24 a are discretely disposed in the formof scattered islands on the transparent conductive film 32, so that, ina position in which the sub-elements 24 a are not disposed, thetransparent conductive film 32 is so exposed in the electrolysis chamber16 a as to come into contact with the aqueous electrolytic solution AQto thereby short-circuit. Furthermore, the lateral faces of the pnjunction element 24 (24 a), that is, the lateral faces of thephotoelectric conversion layer 28, the buffer layer 30 and thetransparent protective film 34 as laminated are also exposed in theelectrolysis chamber 16 a and comes into contact with the aqueouselectrolytic solution AQ, and therefore a short circuit occurs.

Accordingly, it is preferable to cover the surface of the transparentconductive film 32 in portions exposed in the electrolysis chamber 16 a,and the lateral faces of the pn junction element 24 (24 a) as well, witha transparent insulating film 37.

In the element laminate 12, light is incident on the pn junction element24 from the transparent protective film 34 side and passes through thetransparent protective film 34 and the buffer layer 30. As a result, anelectromotive force is generated in the photoelectric conversion layer28, and for example, the migration of a charge (electrons) to thetransparent protective film 34 from the transparent conductive film 32occurs. In other words, an electric current flowing to the transparentconductive film 32 from the transparent protective film 34 is generated(the migration of holes occurs).

On the other hand, light incident on the pn junction element 22 from thetransparent insulating film 37 side passes through the transparentinsulating film 37, the transparent conductive film 32, and the bufferlayer 30. As a result, an electromotive force is generated in thephotoelectric conversion layer 28, and for example, the migration of acharge (electrons) to the transparent conductive film 32 from theconductive plate 26 occurs. In other words, an electric current flowingto the conductive plate 26 from the transparent conductive film 32 isgenerated (the migration of holes occurs).

Therefore, in the element laminate 12, the transparent protective film34 of the pn junction element 24 on the upper side becomes the gasgeneration portion 14 a (cathode electrode for electrolysis) generatinghydrogen, and the conductive plate 26 of the pn junction element 22 onthe lower side becomes the gas generation portion 14 b (anode electrodefor electrolysis) generating oxygen.

The conductive plate 26 is composed of, for example, Mo, and functionsas a substrate supporting the element laminate 12 and as an oxygengeneration surface generating oxygen.

The photoelectric conversion layer 28 is composed of, for example, aCIGS (Copper indium gallium (di)selenide)-based compound semiconductorfilm or a CZTS (Copper zinc tin sulfide)-based compound semiconductorfilm. In the pn junction element 22 on the lower side, the photoelectricconversion layer 28 is formed on the conductive plate 26, and in the pnjunction element 24 on the upper side, the photoelectric conversionlayer 28 is formed on the transparent conductive film 32.

The buffer layer 30 is composed of, for example, a CdS thin film and isformed on the surface of the photoelectric conversion layer 28. At theinterface between the buffer layer 30 and the photoelectric conversionlayer 28, pn junction is formed. Consequently, it can be said that thephotoelectric conversion layer 28 is a thin film of a p-typesemiconductor, and the buffer layer 30 is a thin film of an n-typesemiconductor.

The photoelectric conversion layer 28 and the buffer layer 30 are usedin both the pn junction element 22 on the lower side and the pn junctionelement 24 on the upper side, and at least one of the photoelectricconversion layer 28 and the buffer layer 30 may be the same for both thepn junction elements 22 and 24 or may vary between the pn junctionelements 22 and 24.

The transparent conductive film 32 is composed of, for example, atransparent conductive film such as an IMO (Mo-added In₂O₃) film and isformed on the buffer layer 30. Herein, in the pn junction element 22 onthe lower side, the transparent conductive film 32 functions as an upperelectrode. Accordingly, the transparent conductive film 32 is aconductive film which functions as a light receiving surface on the pnjunction composed of the buffer layer 30 and the photoelectricconversion layer 28 in the pn junction element 22, and also functions asa lower electrode of the pn junction element 24 on the upper side. Thatis, the transparent conductive film 32 functions as a conductive filmwhich connects the pn junction element 22 on the lower side to the pnjunction element 24 on the upper side in series.

The transparent protective film 34 is composed of, for example, atransparent conductive film such as an ITO (Sn-added In₂O₃) film, and isformed on the buffer layer 30 in the pn junction element 24 on the upperside. Herein, the transparent protective film 34 functions as an upperelectrode of the pn junction element 24 on the upper side. Accordingly,the transparent protective film 34 functions as the light receivingsurface on the pn junction composed of the buffer layer 30 and thephotoelectric conversion layer 28 and also functions as the hydrogengeneration surface generating hydrogen.

The conductive plate 26 is constituted with, for example, a metal suchas Mo, Al, Cu, Cr, W, Ni, Ta, Fe or Co, or a combination of thesemetals. The conductive plate 26 may have a single layer structure or alaminated structure such as a double layer structure. The back surfaceof the conductive plate 26 becomes an oxygen gas generation surfacegenerating oxygen and comes into direct contact with an aqueouselectrolytic solution. Therefore, the conductive plate 26 is preferablyof a metal that is not easily oxidized. Particularly, the conductiveplate 26 is preferably constituted with Mo. The film thickness of theconductive plate 26 is generally about 1,000 μm, and preferably 100 μmto 1,500 μm.

The back surface of the conductive plate 26 of the pn junction element22 becomes the gas generation portion 14 b (anode electrode forelectrolysis) generating oxygen, and generates oxygen molecules, thatis, oxygen (oxygen gas) by withdrawing electrons from hydroxide ions OH⁻ionized from water molecules in the aqueous electrolytic solution AQ(2OH⁻→H₂O+O₂/2+2e⁻), that is to say, functions as an oxygen gasgeneration surface.

Accordingly, the back surface of the conductive plate 26 is preferablyinclined toward the downstream side from the upstream side along thestream of the aqueous electrolytic solution AQ such that the generatedoxygen does not stay on the back surface. The direction of theinclination is not particularly limited. When the back surface of theconductive plate 26 is inclined downward toward the downstream side, theoxygen generated on the back surface is highly effectively removed. Whenit is inclined upward toward the downstream side, it is possible tocause the oxygen gas, which floats from the aqueous electrolyticsolution AQ and is concentrated on the back surface of the conductiveplate 26, to flow to a discharge port 40 b together with the aqueouselectrolytic solution AQ with efficiency. In the example as illustrated,a supply port 38 b of the aqueous electrolytic solution AQ is on theright side in the drawing, and the discharge port 40 b for dischargingthe generated oxygen together with the aqueous electrolytic solution AQis on the left side in the drawing. Consequently, in order to rapidlydischarge the generated oxygen, it is better for the back surface of theconductive plate 26 to be inclined upward toward the left side in thedrawing from the right side in the drawing.

If the back surface of the conductive plate 26 is inclined as above, itis possible to rapidly move the generated oxygen from the back surfaceof the conductive plate 26 that serves as the oxygen generation surface,without causing the oxygen to stay on the back surface, and to dischargethe oxygen from the discharge port 40 b together with the aqueouselectrolytic solution AQ. Therefore, it is possible to bring the backsurface of the conductive plate 26 into contact with the aqueouselectrolytic solution AQ at all times, and to generate oxygen withexcellent efficiency by causing a photolysis reaction of water on theentire back surface of the conductive plate 26.

In order to accelerate the generation of oxygen by the photolysisreaction of water, an oxygen generation promoter such as IrO₂, CoO_(x)or the like may be formed in the form of scattered islands on the backsurface of the conductive plate 26 which becomes the oxygen gasgeneration surface.

At the interface between the buffer layer 30 and the photoelectricconversion layer 28, the photoelectric conversion layer 28 forms the pnjunction of which the photoelectric conversion layer 28 side is of aP-type and the buffer layer 30 side is of an N-type. The photoelectricconversion layer 28 absorbs the light reaching it after passing throughthe transparent insulating film 37, the transparent conductive film 32and the buffer layer 30, generates holes on the p-side and electrons onthe n-side, and has a function of photoelectric conversion. In thephotoelectric conversion layer 28, the holes generated in the pnjunction are migrated toward the conductive plate 26 from thephotoelectric conversion layer 28, and the electrons generated in the pnjunction are migrated toward the transparent conductive film 32 from thebuffer layer 30. The film thickness of the photoelectric conversionlayer 28 is preferably 200 nm to 3,000 nm, and particularly preferably500 nm to 2,000 nm.

The photoelectric conversion layer 28 is preferably a compoundsemiconductor-based photoelectric conversion semiconductor layer. Themain component of the photoelectric conversion layer 28 is notparticularly limited (the main component referring to a componentcomprising not less than 20% by mass of the layer). In view of obtaininghigh photoelectric conversion efficiency, a chalcogen compoundsemiconductor, a compound semiconductor having a chalcopyrite structure,and a compound semiconductor having a defect stannite-type structure canbe suitably used as the main component.

Favorable examples of the chalcogen compound (compound containing S, Se,or Te) include:

a II-VI compound such as ZnS, ZnSe, ZnTe, CdS, CdSe or CdTe;

a group I-III-VI₂ compound such as CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂,CuInS₂, CuGaSe₂ or Cu(In, Ga) (S, Se)₂; and

a group I-III₃-VI₅ compound such as Culn₃Se₅, CuGa₃Se₅ or Cu(ln,Ga)₃Se₅.

Favorable examples of the compound semiconductors of a chalcopyrite-typestructure and of a defect stannite-type structure include:

a group I-III-VI₂ compound such as CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂,CuInS₂, CuGaSe₂ or Cu(In, Ga) (S, Se)₂; and

a group I-III₃-VI₅ compound such as CuIn₃Se₅, CuGa₃Se₅ or Cu(In,Ga)₃Se₅.

In the above description, (In, Ga) and (S, Se) represent(In_(1-x)Ga_(x)) and (Si_(1-y)Se_(y)) respectively (here, x=0 to 1, y=0to 1).

The photoelectric conversion layer 28 is preferably constituted with,for example, a CIGS-based compound semiconductor having a chalcopyritecrystal structure or a CZTS-based compound semiconductor, among others.That is, the photoelectric conversion layer 28 is preferably constitutedwith a CIGS layer. The CIGS layer may be constituted not only withCu(In, Ga)Se₂ but also with a known material used in the CIGS-basedmaterial such as CuInSe₂(CIS).

The method for forming the photoelectric conversion layer 28 is notparticularly limited. For example, as the method for forming the CIGSlayer containing Cu, In, Ga, or S, 1) a multi-source vapor depositionmethod, 2) a selenization method, 3) a sputtering method, 4) a hybridsputtering method, and 5) a mechanochemical processing method are known.

Examples of other methods for forming the CIGS layer include a screenprinting method, a close-spaced sublimation method, an MOCVD method, aspraying method (wet film formation method), and the like. For example,by a screen printing method (wet film formation method), a sprayingmethod (wet film formation method) or the like, a fine particle filmcontaining elements of group Ib, group IIIb, and group VIb is formed ona substrate and subjected to thermal decomposition processing(optionally performed in a group VIb element atmosphere), and in thisway, a crystal having a desired composition can be obtained (JP 9-74065A, JP 9-74213 A, and the like).

As described above, in the present invention, the photoelectricconversion layer 28 is preferably constituted with a CIGS-based compoundsemiconductor having a chalcopyrite crystal structure or a CZTS-basedcompound semiconductor, for example. However, the present invention isnot limited thereto, and any photoelectric conversion element may beused as long as it makes it possible to form a pn junction composed ofan inorganic semiconductor and generate hydrogen and oxygen by causing aphotolysis reaction of water. For example, a photoelectric conversionelement utilized in a solar battery cell constituting a solar battery ispreferably used. Examples of such a photoelectric conversion elementinclude a thin film silicon-based thin film-type photoelectricconversion element, a CdTe-based thin film-type photoelectric conversionelement, a dye-sensitized thin film-type photoelectric conversionelement, and an organic thin film-type photoelectric conversion element,in addition to a CIGS-based thin film-type photoelectric conversionelement, a CIS-based thin film-type photoelectric conversion element,and a CZTS-based thin film-type photoelectric conversion element.

The absorption wavelength of the inorganic semiconductor forming thephotoelectric conversion layer 28 is not particularly limited as long asthe absorption wavelength is within a wavelength range allowingphotoelectric conversion. The wavelength range may be any rangeincluding wavelength regions of solar light and the like, particularly,from a visible wavelength region to an infrared wavelength region. Theabsorption wavelength edge of the inorganic semiconductor is preferablyequal to or greater than 800 nm, that is to say, a wavelength rangeincluding up to an infrared wavelength region is preferred. This isbecause more than half of the solar light energy reaching the ground isincluded in an ultraviolet-visible region at wavelengths of not morethan 800 nm, and effective use of such solar energy makes it significantto produce hydrogen energy by the inventive apparatus as an alternativeto fossil fuels.

The buffer layer 30 is so formed as to constitute a pn junction layertogether with the photoelectric conversion layer 28, that is, to form apn junction at the interface between the photoelectric conversion layer28 and the buffer layer 30, to protect the photoelectric conversionlayer 28 at the time of forming the transparent conductive film 32, andto transmit the light incident on the transparent conductive film 32 tothe photoelectric conversion layer 28.

The buffer layer 30 preferably contains a metal sulfide containing atleast one metal element selected from the group consisting of Cd, Zn, Snand In, with specific examples including CdS, ZnS, Zn(S, O) and/or Zn(S,O, OH), SnS, Sn(S, O) and/or Sn(S, O, OH), InS, In(S, O) and/or In(S, O,OH). The film thickness of the buffer layer 30 is preferably 10 nm to 2μm, and more preferably 15 nm to 200 nm. The buffer layer 30 is formedby, for example, a chemical bath deposition process (hereafter referredto as “CBD process”).

A window layer may be disposed between the buffer layer 30 and thetransparent conductive film 32. The window layer is constituted with,for example, a ZnO layer having a thickness of about 10 nm.

The transparent conductive film 32 has light transmitting properties. Inthe pn junction element 22 on the lower side, the transparent conductivefilm 32 brings light into the photoelectric conversion layer 28, andfunctions as an upper electrode that is paired with the conductive plate26 as a lower electrode and moves the holes and electrons generated inthe photoelectric conversion layer 28 (to causes an electric current toflow). Furthermore, the transparent conductive film 32 functions as alower electrode of the pn junction element 24 on the upper side and alsofunctions as a transparent conductive film for directly connecting thepn junction element 22 on the lower side to the pn junction element 24on the upper side such that the pn junction elements 22 and 24 areconnected to each other in series.

The transparent conductive film 32 is constituted with IMO (Mo-addedIn₂O₃), ZnO doped with Al, B, Ga, In or the like, or ITO (indium tinoxide), for example. The transparent conductive film 32 may have asingle layer structure or a laminated structure such as a double layerstructure. The thickness of the transparent conductive film 32 is notparticularly limited, and is preferably 0.1 μm to 2 μm, and morepreferably 0.3 μm to 1 μm.

The method for forming the transparent conductive film 32 is notparticularly limited. The transparent conductive film can be formed by avapor phase film formation method such as an electron beam vapordeposition method, a sputtering method and a CVD method or by a coatingmethod.

The transparent protective film 34 is formed on the upper surface of thebuffer layer 30 in the pn junction element 24 on the upper side and haslight transmitting properties. The transparent protective film 34 bringslight into the photoelectric conversion layer 28, functions as an upperelectrode that is paired with the transparent conductive film 32 as alower electrode and moves the holes and electrons generated in thephotoelectric conversion layer 28 (to causes an electric current toflow), and functions as a transparent conductive film which protects thebuffer layer 30 and the photoelectric conversion layer 28.

In addition, the transparent protective film 34 serves as the gasgeneration portion 14 a (cathode electrode for electrolysis) generatinghydrogen and generates hydrogen molecules, that is, hydrogen (hydrogengas) by supplying electrons to hydrogen ions (protons) H⁺ ionized fromwater molecules (2H⁺+2e⁻→H₂). The surface of the transparent protectivefilm 34 functions as a hydrogen gas generation surface.

As the transparent protective film 34, it is possible to use the sametransparent conductive film as the transparent conductive film 32, suchas ITO (indium tin oxide), ZnO doped with Al, B, Ga, In or the like, orIMO (Mo-added In₂O₃). The transparent protective film 34 may have asingle layer structure or a laminated structure such as a double layerstructure, as the transparent conductive film 32. The thickness of thetransparent protective film 34 is not particularly limited, and ispreferably 10 nm to 200 nm, and more preferably 30 nm to 100 nm.

The method for forming the transparent protective film 34 is notparticularly limited, as is the case with the transparent conductivefilm 32. The transparent protective film 34 can be formed by a vaporphase film formation method such as an electron beam vapor depositionmethod, a sputtering method and a CVD method or by a coating method.

As described above, the transparent protective film 34 functions as anelectrode for generating hydrogen, and the surface thereof functions asa hydrogen gas generation surface. Accordingly, the transparentprotective film 34 functions as the gas generation portion 14 agenerating hydrogen, and the region thereof constitutes a hydrogen gasgeneration region.

On the surface of the transparent protective film 34, the hydrogengeneration promoter 36 for accelerating the generation of hydrogen isformed in the form of scattered islands.

Examples of the hydrogen generation promoter 36 include a componentcomposed solely of Pt (platinum), Pd (palladium), Ni (nickel), Au(gold), Ag (silver), Ru (ruthenium), Cu (copper), Co (cobalt), Rh(rhodium), Ir (iridium), or Mn (manganese), an alloy as a combination ofthese, and an oxide thereof. The size of the hydrogen generationpromoter 36 is not particularly limited, and is preferably 1 nm to 100nm.

The method for forming the hydrogen generation promoter 36 is notparticularly limited, and the hydrogen generation promoter 36 can beformed by a photodeposition method, a sputtering method, an impregnationmethod, or the like.

As in the example illustrated, it is preferable that the hydrogengeneration promoter 36 is provided on the upper surface of thetransparent protective film 34. However, when hydrogen can besufficiently generated, the hydrogen generation promoter 36 may be notprovided.

In the example illustrated, the hydrogen generation promoter 36 isformed and scattered on the upper surface of the transparent protectivefilm 34 formed on the upper surface of the buffer layer 30. However, thepresent invention is not limited thereto. The transparent protectivefilm 34 may not be provided, and the hydrogen generation promoter 36 maybe directly formed and scattered on the upper surface of the bufferlayer 30.

In this case, the buffer layer 30 functions as an N-type semiconductorand as an electrode for generating hydrogen, and the surface thereoffunctions as a hydrogen gas generation surface. Therefore, the bufferlayer 30 functions as the gas generation portion 14 a generatinghydrogen, and the region thereof constitutes a hydrogen gas generationregion.

The transparent insulating film 37 has light transmitting properties.For protecting the pn junction elements 22 and 24, specifically, forprotecting the portion outside the hydrogen gas generation regions inthe electrolysis chamber 16 a, the transparent insulating film 37 is soprovided as to cover the portion outside the gas generation regions.Specifically, the transparent insulating film 37 covers the portion ofthe surface of the transparent conductive film 32 that does not have thepn junction element 24 on the upper side formed therein and,accordingly, serves as the light receiving surface of the pn junctionelement 22 on the lower side, and all the lateral faces of theindividual sub-elements 24 a constituting the pn junction element 24.

The transparent insulating film 37 is constituted with, for example,SiO₂, SnO₂, Nb₂O₅, Ta₂O₅, Al₂O₃, Ga₂O₃ or the like. The thickness of thetransparent insulating film 37 is not particularly limited, and ispreferably 100 nm to 1,000 nm.

The method for forming the transparent insulating film 37 is notparticularly limited. The transparent insulating film 37 can be formedby an RF sputtering method, a DC reactive sputtering method, an MOCVDmethod or the like.

The region of the transparent conductive film 32, in which thetransparent insulating film 37 is formed while the pn junction element24 on the upper side is not formed, serves as the light receivingsurface of the pn junction element 22 on the lower side. In contrast, ineach of the sub-elements 24 a of the pn junction element 24 on the upperside, the buffer layer 30 or the transparent protective film 34 of therelevant sub-element serves as the light receiving surface.Consequently, in order to generate hydrogen and oxygen with excellentefficiency by a photolysis reaction of water, according to the abilityof the pn junction elements 22 and 24, for example, according to theelectromotive force or the amount of electrons or holes generated, apredetermined balance needs to be achieved between the total lightreceiving area of the pn junction element 24 on the upper side, that is,the total area of the light receiving surfaces of all the sub-elements24 a, and the total light receiving area of the pn junction element 22on the lower side, that is, the total area of the region of thetransparent conductive film 32 in which the pn junction element 24 onthe upper side is not formed. For example, when the pn junction elements22 and 24 are equal in ability, they are preferably also equal in totallight receiving area.

Therefore, it is preferable that the total light receiving areas of thepn junction elements 22 and 24 are balanced according to their ability.

The element laminate 12 is constituted as above.

The element laminate 12 can be manufactured by the followingmanufacturing method, but the present invention is not limited thereto.

FIG. 3 is a flowchart showing an example of a process of manufacturingthe gas production apparatus shown in FIGS. 1 and 2.

First, in Step S100, as the conductive plate 26, for example, a Mosubstrate is prepared.

Thereafter, in Step S102, on one surface of the conductive plate 26, asthe photoelectric conversion layer 28, for example, a CIGS-basedcompound semiconductor film (P-type semiconductor layer) is formed by aknown method such as a selenization/sulfuration method or a multi-sourcesimultaneous vapor deposition method.

Then, in Step S104, on the photoelectric conversion layer 28 formed asabove, as the buffer layer 30, for example, a CdS film (N-typesemiconductor layer) is formed by a known method such as a CBD (chemicalbath deposition) process.

Subsequently, in Step S106, on the buffer layer 30 formed as above, asthe transparent conductive film 32, for example, an ITO film whichbecomes a transparent conductive layer is formed by a known method suchas an MOCVD method or an RF sputtering method.

Thereafter, in Step S108, on the transparent conductive film 32 formedas above, as the photoelectric conversion layer 28, for example, aCIGS-based compound semiconductor film (P-type semiconductor layer) isformed in the same manner as in Step S102.

Then, in Step S110, on the photoelectric conversion layer 28 formed asabove, as the buffer layer 30, for example, a CdS film (N-typesemiconductor layer) is formed in the same manner as in Step S104.

Subsequently, in Step S112, on the buffer layer 30 formed as above, asthe transparent protective film 34, for example, a ZnO film whichbecomes a protective layer is formed by a known method such as an MOCVDmethod or an RF sputtering method.

After that, in Step S114, a structure A (pn junction element 24 on theupper side) composed of the photoelectric conversion layer 28(CIGS-based compound semiconductor film), the buffer layer 30 (CdSfilm), and the transparent protective film 34 (ZnO film) formed as aboveis cut by a mechanical scribing method, thereby forming a group ofstructures A (a group of sub-elements 24 a) that are discretelydisposed.

Then, in Step S116, on the group of structures A formed as above, as thetransparent insulating film 37, for example, a SiO₂ film which becomes atransparent insulating layer is formed by a known method such as anMOCVD method, an RF sputtering method, or a DC reactive sputteringmethod. Subsequently, by a known method such as a CMP method, thetransparent insulating film 37 (SiO₂ film) formed on the upper surfaceportion of the structures A is selectively scraped off such that thetransparent protective film 34 (ZnO film), which becomes a protectivelayer, is exposed only on the upper surface portion of the sub-elements24 a (structures A) as the pn junction element 24.

Finally, in Step S118, only on the transparent protective film 34exposed on the upper surface portion of the pn junction element 24(sub-elements 24 a) (structures A), as the hydrogen generation promoter36, for example, a Pt promoter is supported by a known method such as aphotodeposition method.

In this way, the element laminate 12 can be manufactured.

The container 18 houses the element laminate 12 and constitutes theelectrolysis chamber 16 composed of the electrolysis chamber 16 a on theupper side, which contains (retains) the aqueous electrolytic solutionAQ in contact with the upper surface of the transparent protective film34 of the pn junction element 24 a on the upper side constituting thegas generation portion 14 a, contains (retains) hydrogen as the gasgenerated from the gas generation portion 14 a, and is provided on theupper side of the element laminate 12, and the electrolysis chamber 16 bon the lower side, which contains (retains) the aqueous electrolyticsolution AQ in contact with the back surface of the conductive plate 26of the pn junction element 22 at the lower end constituting the gasgeneration portion 14 b, contains (retains) oxygen as the gas generatedfrom the gas generation portion 14 b, and is provided on the lower sideof the element laminate 12.

As shown in FIG. 2, the electrolysis chamber 16 a on the upper side andthe electrolysis chamber 16 b on the lower side communicate with eachother in a region that surrounds the outer periphery of the elementlaminate 12 along the inner surface of the container 18, and a diaphragm20 is disposed in the region in which the electrolysis chambers 16 a and16 b communicate with each other.

A plurality of (three in the example illustrated in the drawings) supplyports 38 a for supplying the aqueous electrolytic solution AQ into theelectrolysis chamber 16 a are provided in an upper part of a lateralface on the right side in FIG. 1 of the electrolysis chamber 16 a in thecontainer 18 (on the upper right side of the apparatus). Furthermore, aplurality of (four in the example illustrated in the drawings) dischargeports 40 a for discharging the aqueous electrolytic solution AQ in theelectrolysis chamber 16 a and a plurality of (three in the exampleillustrated in the drawings) collection ports 42 for collecting hydrogengenerated in the electrolysis chamber 16 a are both provided in an upperpart of a lateral face on the left side in FIG. 1 of the electrolysischamber 16 a in the container (on the upper left side of the apparatus).

A plurality of (two in the example illustrated in the drawings) supplyports 38 b for supplying the aqueous electrolytic solution AQ into theelectrolysis chamber 16 b are provided in a lower part of a lateral faceon the right side in FIG. 1 of the electrolysis chamber 16 b in thecontainer 18 (on the lower right side of the apparatus). Furthermore, aplurality of (two in the example illustrated in the drawings) dischargeports 40 b for discharging the aqueous electrolytic solution AQ in theelectrolysis chamber 16 b together with oxygen generated in theelectrolysis chamber 16 b are provided in a lower part of a lateral faceon the left side in FIG. 1 of the electrolysis chamber 16 b in thecontainer 18 (on the lower left side of the apparatus). The oxygendischarged from the discharge ports 40 b together with the aqueouselectrolytic solution AQ is collected by a collection portion not shownin the drawings.

Both the supply ports 38 a and the discharge ports 40 a are provided ina position slightly above the position of the transparent protectivefilm 34, such that a water flow, which prevents the hydrogen generatedby the transparent protective film 34 of the pn junction element 24 (agroup of the sub-elements 24 a) from staying on the surface of thetransparent protective film 34, can be generated in the electrolysischamber 16 a. Therefore, it is possible to bring the surface of thetransparent protective film 34 into contact with the aqueouselectrolytic solution AQ at all times, and to generate hydrogen withexcellent efficiency. It goes without saying that the position of thesupply ports 38 a and the discharge ports 40 a is the same as theposition of the surface of the aqueous electrolytic solution AQ in theelectrolysis chamber 16 a.

In contrast, both the supply ports 38 b and the discharge ports 40 b areplaced in the position of the back surface of the conductive plate 26that constitutes the ceiling of the electrolysis chamber 16 b and isinclined upward toward the downstream side.

In the electrolysis chamber 16 a, hydrogen is retained above the surfaceof the aqueous electrolytic solution AQ. Therefore, the ceiling of theelectrolysis chamber 16 a is constituted such that it is inclined upwardtoward the downstream side, as the back surface of the conductive plate26, and is separated from the surface of the aqueous electrolyticsolution AQ. Furthermore, in order to collect the retained hydrogen withexcellent efficiency, the collection ports 42 are provided in a positionslightly above the position of the surface of the aqueous electrolyticsolution AQ, that is, a position slightly above the position of thesupply ports 38 a and the discharge ports 40 a.

The number of the supply port 38 a, the discharge port 40 a, and thecollection port 42 is not particularly limited, and may be arbitrarilyset as long as a water flow, which prevents the hydrogen from staying onthe hydrogen gas generation surface, can be generated. However, it ispreferable to provide a required number of the supply ports 38 a, thedischarge ports 40 a, and the collection ports 42 in a position ensuringa water flow on the surface of the pn junction element 24 (a group ofthe sub-elements 24 a).

The number of the supply ports 38 b and the discharge ports 40 b is notparticularly limited either, and may be arbitrarily set as long as awater flow, which prevents the oxygen from staying on the oxygen gasgeneration surface, can be generated. However, it is preferable toprovide a required number of the supply ports 38 b and the dischargeports 40 b in a position ensuring a water flow on the back surface ofthe conductive plate 26 of the pn junction element 22.

In order that the hydrogen generated in the electrolysis chamber 16 aand the oxygen generated in the electrolysis chamber 16 b may beseparately collected at high purity, and that the hydroxide ionsincreased as a result of the generation of hydrogen in the electrolysischamber 16 a (with increased pH) and the hydrogen ions increased as aresult of the generation of oxygen in the electrolysis chamber 16 b(with reduced pH) may permeate the diaphragm 20 to cause neutralization,the diaphragm 20 separates the electrolysis chamber 16 in the container18 into the electrolysis chamber 16 a and the electrolysis chamber 16 b.The diaphragm 20 is a membrane permeable to ions but impermeable to gas.

As described above, the diaphragm 20 is disposed in a region surroundingthe outer periphery of the element laminate 12 along the inner surfaceof the container 18, in which region the electrolysis chamber 16 a onthe upper side and the electrolysis chamber 16 b on the lower sidecommunicate with each other. The diaphragm 20 is attached to the innerwall surface of the container 18 and the outer wall surface of theelement laminate 12 in a state of coming into close contact with thesewithout a void. As a result, the diaphragm 20 can separate the region ofthe electrolysis chamber 16 a, which comes into contact with the pnjunction element 24 on the upper side, from the region of theelectrolysis chamber 16 b, which comes into contact with the pn junctionelement 22, such that the permeation of gas does not occur while thepermeation of ions occur.

The diaphragm 20 is constituted with, for example, an ion exchangemembrane, a ceramic filter, or Vycor glass. The thickness of thediaphragm 20 is not particularly limited, and is preferably 10 μm to1,000 μm.

The gas production apparatus of the present invention is basicallyconstituted as above.

The gas production apparatus of the present invention has beenspecifically described, but the present invention is not limited to theaforementioned examples. It goes without saying that the presentinvention can be improved or modified in various ways without departingfrom the gist and scope of the present invention.

EXAMPLES

Hereinafter, the gas production apparatus of the present invention willbe specifically described based on the following Examples, to which thepresent invention is not limited.

Example 1

First, as Example 1, the gas production apparatus 10 shown in FIG. 1that was constituted as below was prepared, the electrolysis chamber 16was filled with an aqueous electrolytic solution, the apparatus wasirradiated with light, and the amount of the generated hydrogen gas andoxygen gas was evaluated.

The results are shown in Table 1.

The element laminate 12 of the gas production apparatus 10 of Example 1was prepared according to the preparation flow shown in the flowchart ofFIG. 3.

1. Constitution of hydrogen generation element (pn junction element 24(sub-elements 24 a)).

Transparent conductive film: IMO (Mo-added In₂O₃), a thickness of 1,000nm

P-type semiconductor thin film: CIGS, a thickness of 500 nm

N-type semiconductor thin film: CdS, a thickness of 50 nm

Protective film: ITO (Sn-added In₂O₃), a thickness of 50 nm

Promoter: Pt

2. Constitution of oxygen generation element (pn junction element 22).

Conductive plate: Mo, a thickness of 1 mm

P-type semiconductor thin film: CIGS, a thickness of 2,000 nm

N-type semiconductor thin film: CdS, a thickness of 50 nm

3. Form of conductive plate.

Shape on oxygen gas generation side: processed to be inclined toward theflow direction of oxygen gas (no oxygen gas bubbles staying)

4. Form of oxygen generation element.

Size: 15 cm×20 cm

5. Form of hydrogen generation element.

Size: 3 cm to 5 cm for each side

Number of elements: nine (two or more)

Disposition of elements: the respective elements are discretelydisposed.

6. Others

Diaphragm: Nafion (substance permeable to ions but impermeable to gas)

Aqueous electrolytic solution: 0.1M Na₂SO₄ solution (pH 9.5)

Promoter: Pt particles (size: up to 20 nm in diameter)

Material for container (module): glass

Light source for irradiation: irradiation with simulated solar light ofAM 1.5.

Comparative Example 1

As Comparative Example 1, a gas production apparatus of the sameconstitution as that of Example 1 was prepared except that the hydrogengeneration portion and the oxygen generation portion were formed in thesame element. The prepared gas production apparatus was irradiated withlight in the same manner as in Example 1, and the amount of thegenerated gas was evaluated.

The results are shown in Table 1.

Comparative Example 2

Next, as Comparative Example 2, a gas production apparatus of the sameconstitution as that of Example 1 was prepared except that the hydrogengeneration element and the oxygen generation element have the same size(15 cm×20 cm), and the apparatus was constituted with one hydrogengeneration element and one oxygen generation element. The prepared gasproduction apparatus was irradiated with light in the same manner as inExample 1, and the amount of the generated gas was evaluated.

The results are shown in Table 1.

The evaluation was performed as below.

As the amount of gas generated (initial stage), the amount of gasgenerated immediately after the start of light irradiation was measured.

As the amount of gas generated (after a passage of time), the amount ofgas generated 24 hours after the start of light irradiation wasmeasured.

In Table 1, “A” of the column of comprehensive determination indicates acase in which both the amount of hydrogen gas generated (initial stage)and the amount of hydrogen gas generated (after a passage of time)exceeded 50 ml/min·m², while “B” of the column of comprehensivedetermination indicates a case in which either or both of the amount ofhydrogen gas generated (initial stage) and the amount of hydrogen gasgenerated (after a passage of time) were less than 50 ml/min·m². Basedon such determination criteria, the evaluation was made. Herein, thestandard value of 50 ml/min·m² is a numerical value converted based on asolar light conversion efficiency of 1%.

TABLE 1 Amount of hydrogen Amount of hydrogen gas generated (after gasgenerated a passage of Comprehensive (initial stage) time) determinationExample 1 65 ml/min · m² 55 ml/min · m² A Comp.  0 ml/min · m²  0 ml/min· m² B Example 1 Comp. 55 ml/min · m² 30 ml/min · m² B Example 2

As shown in Table 1, in Example 1 of the present invention, the amountof hydrogen gas generated immediately after the start of lightirradiation was 65 ml/min·m², and the amount of hydrogen gas generatedafter 24 hours was 55 ml/min·m². Because the generated hydrogen gasbubbles adhered to part of the hydrogen generation portion on the lightreceiving surface side, the contact area between the hydrogen generationportion and the solution was reduced due to the bubbles, and as aresult, the gas generation efficiency was reduced, and the amount of gasgenerated after 24 hours was reduced compared to the initial stage.However, by discretely disposing the hydrogen generation elements, aturbulent flow occurred in the water introduced into the apparatus, andin this way, most of the bubbles could be removed.

In Comparative Example 1, the amount of hydrogen gas generatedimmediately after the start of light irradiation was 0 ml/min·m², andthe generation of gas could not be detected. Furthermore, the amount ofhydrogen gas generated was still 0 ml/min·m² even after 24 hours, andthe generation of gas could not be detected.

In Comparative Example 2, the amount of hydrogen gas generatedimmediately after the start of light irradiation was 55 ml/min·m².Because the element for generating hydrogen gas covered the entirety ofthe element for generating oxygen gas, the amount of light reaching theelement for generating oxygen gas was reduced, and accordingly, thetotal gas generation ability of the system was reduced. Furthermore, theamount of hydrogen gas generated after 24 hours was 30 ml/min·m².Because the generated hydrogen gas bubbles covered the entire lightreceiving surface, light was scattered due to the bubbles, andaccordingly, the amount of incident light was reduced, and the gasgeneration efficiency was markedly reduced.

As is evident from the above results, in Example 1 of the presentinvention, a large amount of gas was generated immediately after thestart of light irradiation, and the amount of gas generated could bemaintained at a high level even after a passage of time. Therefore, itis understood that gas could be stably generated.

In contrast, it is understood that, in Comparative Example 1, apotential (electromotive force) necessary for decomposing water intohydrogen and oxygen could not be obtained.

Moreover, it is understood that, in Comparative Example 2, although alarge amount of gas was generated immediately after the start of lightirradiation, the amount of gas generated was markedly reduced after apassage of time, and gas could not be stably generated. The aboveresults show the superiority of Example 1 of the present invention.

The above results clearly show the effects of the present invention.

What is claimed is:
 1. A gas production apparatus, comprising: anelement laminate in which a plurality of elements, each having a lightreceiving portion and including a semiconductor thin film with pnjunction, are so laminated on each other as to connect in series to eachother; a hydrogen gas generator which is formed on a surface of a firstelement among the plurality of elements and generates hydrogen gas, thefirst element being positioned at one end of the element laminate; afirst electrolysis chamber which includes the hydrogen gas generator andcontains an aqueous electrolytic solution in contact with the hydrogengas generator, and the hydrogen gas generated; an oxygen gas generatorthat is formed on a back surface of a conductive substrate, on which thesemiconductor thin film of a second element among the plurality ofelements is formed, and generates oxygen gas, the second element beingpositioned at another end of the element laminate; a second electrolysischamber which includes the oxygen gas generator and contains an aqueouselectrolytic solution in contact with the oxygen gas generator, and theoxygen gas generated; and a diaphragm which is ion-permeable butgas-impermeable, and is provided between the first electrolysis chamberand the second electrolysis chamber.
 2. The gas production apparatusaccording to claim 1, wherein the hydrogen gas generator is providedwith a hydrogen generation surface, and the hydrogen generation surfaceis formed on a surface of the semiconductor thin film of the firstelement.
 3. The gas production apparatus according to claim 1, whereinthe first element is composed of a plurality of sub-elements, and theplurality of sub-elements are disposed on the second element discretelywith respect to the second element.
 4. The gas production apparatusaccording to claim 3, wherein the plurality of sub-elements each have anelement area smaller than that of the second element.
 5. The gasproduction apparatus according to claim 1, wherein: the oxygen gasgenerator is provided with an oxygen generation surface formed on theback surface of the conductive substrate; and the oxygen generationsurface is inclined upward along a flow direction of the aqueouselectrolytic solution in the second electrolysis chamber.
 6. The gasproduction apparatus according to claim 1, wherein the semiconductorthin film includes a CIGS-based compound semiconductor.
 7. The gasproduction apparatus according to claim 1, wherein the semiconductorthin film includes a CZTS-based compound semiconductor.
 8. The gasproduction apparatus according to claim 1, wherein the semiconductorthin film has an absorption wavelength edge equal to or greater than 800nm.
 9. The gas production apparatus according to claim 1, furthercomprising a hydrogen generation promoter provided on the hydrogengeneration surface of the hydrogen gas generator.
 10. The gas productionapparatus according to claim 9, wherein the hydrogen generation promoteris platinum.